Process for the Manufacture of Self-Binding Pigmentary Particles, Dry or in Aqueous Suspension or Dispersion, Containing Inorganic Matter and Binders

ABSTRACT

The invention concerns a process for the manufacture of self-binding pigmentary particles, dry or in aqueous suspension or dispersion, containing at least one inorganic matter and at least one binder, where the said process comprises the following stages: a) forming one or more aqueous suspensions of at least one inorganic matter and introducing them into a mill with a view to stage c), b) forming or taking one or more aqueous solutions or suspensions or emulsions of at least one binder and introducing them into a mill with a view to stage c), c) co-grinding the aqueous suspension or suspensions obtained in stage a) with the aqueous solutions or suspensions or emulsions obtained in stage b) so as to obtain an aqueous suspension of self-binding pigmentary particles, d) possibly co-grinding the aqueous suspension or dispersion obtained in stage c) with one or more aqueous solutions or suspensions or emulsions of at least one binder, e) possibly drying the aqueous suspension obtained in stage c) or in stage d). f) increasing the concentration of the aqueous suspension obtained at stage c) or d) through thermal or mechanical concentration, g) dispersing the aqueous suspension obtained at stage f) through using at least one dispersing agent and/or at least one wetting agent.

The invention concerns a process for the manufacture of self-bindingpigmentary particles, dry or in aqueous suspension or dispersion,containing at least one inorganic matter and at least one binder.

Inorganic particles and the polymer binders are two of the essentialcomponents used in the manufacture of various coatings; the inorganicparticles, generally calcium carbonate, contribute to the final productcertain properties such as optical properties, and the binders,generally in the form of latex suspensions or dispersions, give anoverall cohesion to all the constituent elements used in the process tomanufacture coating compositions.

However, it has been known for many years that complex interactions mayoccur between the calcium carbonate and all the forms of binders,causing the final properties of the coating products to be modified. Forexample, “Physical and chemical modifications in latex binders and theireffect on the coating colour rheology” (Advanced Coating FundamentalsSymposium, San Diego, Calif., United States, May 4-5, 2001, pp. 108-123)concerns the influence of the physical and chemical modifications in adispersion of styrene-butadiene binders on the rheological properties ofa wet pigmentary coating composition.

For a long time the production of self-binding pigmentary particles hasbeen sought: solid particles containing a polymeric binder and aninorganic pigment which act as a single material, thus preventing theend user from losing specifications due to undesirable interactions invarious applications.

It was initially advanced that such self-binding pigments differ fromthe well-known pigmentary granulates through the nature of the forcesassuring cohesion of these composite particles.

For example, document WO 01/00712 presents dry pigmentary granulatescomprising 5% to 99% by weight of organic polymer pigment, from 0% to94.5% by weight of inorganic pigment and from 0.5% to 5% by weight of abinder or mixture of binders.

Such granulates are manufactured by mixing all the constituents indispersion and by drying by spraying of the said dispersion.

In addition, document WO 01/00713 describes plastic polymer pigments,applicable in a dry form, which can be hollow or solid, containing apolymer, a binder and an inorganic pigment.

As the inventors mention themselves, the conglomerates obtained consistof individual spherical particles bound together by electrostaticforces.

According to a different viewpoint, the concept of self-binding pigmentsmust be considered in this document as mutually bound individualparticles, in which the binding mechanisms use not only electrostaticforces but also chemical bindings created through sorption chemistrymechanisms, or physical bindings such as acid-base interactions betweenthe inorganic matter and the polymeric binders and Lifhshitz/van derWaals interactions.

In accordance with this concept, document WO 93/11183 describes aprocess to prepare stable aqueous dispersions by forming two aqueoussuspensions of inorganic matter and polymeric latex particles, byadjusting the Zeta potential of the suspensions, and finally by mixingthe two suspensions. The Zeta potential may be modified through the useof an additive allowing the surface charge to be adjusted. The polymericlatex binder is supposed to be adsorbed strongly on the inorganic matterparticles.

In addition, document WO 93/12183 teaches a process for the preparationof aqueous dispersions of composite particles comprising a latex and aninorganic matter, used in paints and coatings. The said polymeric latexparticles act as a binder, contributing the necessary spacing betweenthe inorganic particles to give the end product opacity and thebrightness. The process is characterized in that the latex prepared bypolymerisation in emulsion is mixed in an aqueous suspension ofinorganic matter, which suspension of inorganic matter is pre-dispersedwith poly(meth)acrylic acid or its salts, or copolymer polyelectrolytesof (meth)acrylic acid-or its salts. The authors suppose that thedispersant of the pigment does not cover the entire surface of theinorganic matter, and that at least one portion of the said surface isavailable for the adsorption of the polymeric latex particles.

Finally, document U.S. Pat. No. 4,025,483 describes a process toincrease the stability of titanium dioxide aqueous suspensions, bymixing the latter with polymeric latex particles. According to theexamples, the polymeric latex particles increase the effectiveness ofthe dispersing agent which is contained in the initial inorganic mattersuspension.

In the light of the prior art, the pigment-polymer particles can beobtained according to various processes which always make reference tothe use of a third constituent, such as a dispersing agent or anadditive allowing the surface charge to be adjusted, to formulate theinitial aqueous suspensions which contain the inorganic matter on theone hand, and the polymeric compounds on the other, and which are latermixed. Introducing a third constituent may have the result of modifyingdrastically the end properties of the coating in which thepigment-polymer particles are incorporated.

In the present invention a process has been discovered in a surprisingmanner for the preparation of self-binding pigmentary particles, dry orin aqueous suspension or dispersion, containing at least one inorganicmatter and at least one polymeric binder, using a ball mill.

Firstly, this process is different from the simple mixing described indocument WO 03/74786.

Secondly, the process according to the invention spares the skilled manin the art from using a third constituent during the preparation of theaqueous suspensions containing the inorganic matter and the binders, andduring the co-grinding stage.

In addition, and in.a surprising manner, the binders do not adhere anddo not block the mill, such that soiling of the equipment may besatisfactorily controlled.

Finally, another object of the invention resides in the self-bindingpigmentary particles in the dry form obtained by the process accordingto the invention, containing at least one inorganic matter and at leastone binder.

The term binder used in the present application refers to any natural orsynthetic product of an organic nature, having binding properties. Thesebinding properties, which increase the inter-particle cohesion forces ofthe initial mineral, are determined according to the method described inexample 1 of the present application.

According to the object of the invention, the process for thepreparation of self-binding pigmentary particles, dry or in aqueoussuspension or dispersion, comprises the following stages:

-   -   a) forming one or more aqueous suspensions of at least one        inorganic matter and introducing it or them into a mill with a        view to stage c),    -   b) forming or taking one or more aqueous solutions or        suspensions or emulsions of at least one binder and introducing        it or them into a mill with a view to stage c),    -   c) co-grinding the aqueous suspension or suspensions obtained in        stage a) with the aqueous solutions or suspensions or emulsions        obtained in stage b) so as to obtain an aqueous suspension of        self-binding pigmentary particles,    -   d) possibly co-grinding the aqueous suspension obtained in        stage c) with one or more aqueous solutions or suspensions or        emulsions of at least one binder,    -   e) possibly drying the aqueous suspension obtained in stage c)        or in stage d).

According to the invention, the aqueous suspension formed in stage a) ischaracterized in that it contains from 1% to 80% by dry weight ofinorganic matter, and more preferentially from 15% to 60% by dry weightof inorganic matter.

The aqueous suspension formed in stage a) may contain one or moreinorganic matter, notably metal oxides, hydroxides, sulphites, silicatesand carbonates, such as calcium carbonate, dolomites, kaolin, talc,gypsum, titanium dioxide, satin white or aluminium trihydroxide andtheir mixtures. Preferentially it contains calcium carbonate, in anatural form or precipitated form, and more preferentially naturalcalcium carbonate, and very preferentially a natural calcium carbonatechosen from among chalk, marble, calcite or their mixtures.

According to the invention, the aqueous solution(s) or suspension(s) oremulsion(s) formed in stage b) are characterized in that they containfrom 1% to 50% by weight of at least one binder, and more preferentiallyfrom 5% to 20% by weight of at least one binder.

The aqueous solution(s) or suspension(s) or emulsion(s) formed in stageb) are also characterized in that the binder is chosen from among thesemi-crystalline latexes, and preferentially from among the emulsions ofpolyethylene waxes or copolymers in their neutralised polyethylene formwith other monomer units such as acrylic acid or other monomers or theirmixtures, or from among the latexes in emulsion or solutions of solublebinders such as polyvinylic alcohol, polyvinyl acetate, starch, casein,proteins, carboxymethyl cellulose (CMC), ethyl hydroxyethyl cellulose(EHEC) or others, or their mixtures.

According to this variant, the semi-crystalline latexes arepreferentially chosen from among the emulsions of polyethylene wax orthe copolymers in their neutralised polyethylene form with other monomerunits such as acrylic acid or other monomers or their mixtures, and thelatexes in emulsion are preferentially chosen from among the copolymersof acrylic esters.

According to stage c) of the process according to the invention, theaqueous suspension(s) obtained in stage a) and the aqueous solution(s)or suspension(s) or emulsion(s) obtained in stage b) are then co-groundin order to obtain an aqueous suspension of self-binding pigmentaryparticles comprising at least one inorganic matter and at least onebinder.

According to stage d) of the process according to the invention, theaqueous suspension of self-binding pigmentary particles obtained instage c) is then co-ground with one or more aqueous solution(s) orsuspension(s) or emulsion(s) comprising at least one binder.

The Applicant has been able to observe that the binders adsorb to thesurface of the mineral matter, thus creating chemical and physical bondscharacteristic of self-binding particles, without having to use adispersing agent or a third additive, as is illustrated by the figuresof the different examples.

The co-grinding process is undertaken by all the techniques well knownto the skilled man in the art.

According to the invention, the aqueous suspension obtained in stage c)or in stage d) is characterized in that the ratio between the inorganicmatter and the binders contained in the suspension obtained is between99 and 1 expressed as weight proportions, and preferentially between 70and 30 expressed as weight proportions.

Preferentially, the composition of the said aqueous suspension isbetween 5% and 80% by weight of inorganic matter, between 1% and 30% byweight of binders, and between 19% and 94% by weight of water. Morepreferentially, the said aqueous suspension contains between 20% and 40%by weight of inorganic matter, between 5% and 20% by weight of binders,and between 40% and 75% by weight of water.

In addition, according to a variant of the process according to theinvention, a preferential form of the aqueous suspension formed in stagec) or in stage d) is characterized in that the self-binding pigmentaryparticles have an average particle diameter of between 0.1 μm and 10 μm,and preferentially between 0.1 μm and 2 μm, measured using aMasterSizer™ S granulometer sold by the company MALVERN.

This aqueous suspension or dispersion obtained in stage c) of theprocess according to the invention is self-binding, as is shown byexample 1.

A possible variation of the process according the invention ischaracterized in that, after stage c) or possibly stage d), the twostages:

-   -   f) Increasing the concentration of the aqueous suspension        obtained at stage c) or d) through thermal or mechanical        concentration;    -   g) Dispersing the aqueous suspension obtained at stage f)        through using at least one dispersing agent and/or at least one        wetting agent.

According to this variant, the said dispersing agent or agents areselected from among the acrylic or vinylic or allyl polymers and/orcopolymers, such as for example homopolymers or copolymers, in theirtotally acid or partially neutralised or totally neutralised form, usingneutralisation agents containing monovalent or polyvalent cations oramines or their mixtures, of at least one of the monomers such as theacrylic and/or methacrylic, itaconic, crotonic, ftimaric acids, maleicor isocrotonic acid, aconitic, mesaconic, sinapic, undecylenicanhydrides, angelic acid, and/or their respective esters, such as theacrylates and methacrylates of alkyl, of aryl, of alkylaryl, ofarylalkyl and in particular ethyl acrylate, butyl acrylate, methylmethcrylate, acrylamido methyl propane sulphonic acid, acrylamide and/ormethacrylamide, acrylate phosphate of glycol ethylene, methacrylatephosphate of glycol ethylene, acrylate phosphate of glycol propyleneacrylate, methacrylate phosphate of glycol propylene, methacrylamidopropyl trimethyl ammonium chloride or sulphate, ethyl chloride orammonium trimethyl methacrylate sulphate, together with their acrylateand acrylamide counterparts, whether or not quatemised, and/ordimethyldiallyl chloride, vinylpyrrolidone, vinylcaprolactame,diisobutylene, vinyl acetate, styrene, alpha-methyl-styrene, sodiumsulfonate styrene, vinylmethylether, and allylamine.

This or these dispersing agents can also be chosen from among at leastone of the said monomers or their mixtures, polymerised in the presenceof at least one mineral matter.

In addition, it should be noted that the optimisation of the molecularweight of this or these dispersing agents depends on their chemicalnature.

In addition, the said aqueous dispersion of self-binding pigmentaryparticles contains between 0.01% and 2% by weight of dispersing agents.

According to this variant, the aqueous dispersion of self-bindingpigmentary particles contains between 0.01% and 5% by weight of wettingagents.

In a final stage e) of the process according to the invention, theaqueous suspension or dispersion obtained in stage c) or in stage d) maybe dried, so as to obtain self-binding pigmentary particles in a dryform, containing at least one inorganic matter and at least one binder,and possibly at least one dispersing agent and at least one wettingagent.

This stage is accomplished by all known drying methods, andpreferentially by a method of drying by spraying in a diluted medium.

In the process according to the invention, the result of stage e)consists in self-binding pigmentary particles in a dry form, containingat least one inorganic matter and at least one binder, characterized inthat they contain between 70% and 97.5% by weight of inorganic matter,and between 2.5% and 30% by weight of binders, and more preferentiallybetween 85% and 95% by weight of inorganic matter and between 5% and 15%by weight of binders.

In addition, in a variant and according to a preferred form, the averagediameter of the said self-binding pigmentary particles is between 5 μmand 100 μm, and more preferentially between 10 μm and 30 μm, measuredusing a MasterSizer™ S granulometer sold by the company MALVERN.

The invention is now illustrated through examples which cannot limit itsscope.

EXAMPLE 1

This example concerns the process for preparing self-binding pigmentaryparticles in an aqueous suspension from marble and two suspensions ofbinders.

To accomplish this, the first stage a) of the process consists informing an aqueous suspension of 1000 grams by dry weight of marblehaving an average particle diameter of 0.8 lm by putting the marble intosuspension in water at a dry matter content by weight equal to 20%.

Stage b) of the process is this accomplished by diluting an aqueoussuspension of binder Acronal™ 728 sold by the company BASF up to a drymatter content by weight equal to 20%.

Stage c) is accomplished by the successive introduction of the marblesuspension and the binder suspension in a mill of the Dyno-Mill™ typewith a fixed cylinder, a rotating pulser, the grinding body of whichconsists in glass balls with a diameter of between 1.0 mm and 1.4 mm.

After 16 minutes' grinding, stage d) is continued through the additioninto the mill of a second aqueous suspension of binder obtained bydilution, up to a dry matter content by weight equal to 20% of Polygen™WE4 sold by the company BASF.

The total volume occupied by the grinding body is equal to 460 cm³ whileits weight is equal to 820 g.

The grinding chamber has a volume of 600 cm³

The circumferential speed of the mill is 10 m.s⁻¹.

The calcium carbonate suspension is recycled at a rate of 33litres/hour.

The temperature during each grinding test is maintained at approximately25° C.

On conclusion of the grinding (85 minutes) a sample of the obtainedsuspension of self-binding pigmentary particles is removed in a flask.The granulometry of the suspension is measured using a MasterSizer™ Sgranulometer sold by the company MALVERN™ and is such that 85% of theparticles have an average diameter of less than or equal to 1 μm.

The product thus obtained is an aqueous suspension of self-bindingpigmentary particles having a dry matter by weight content of calciumcarbonate equal to 20%, an average particle diameter equal to 0.5 μmmeasured using a MasterSizer™ S granulometer, and a marble/Acronal™S728/Polygen™ WE4 ratio equal to 100/9.5/0.5 by dry matter weightproportions.

In this example, the illustration of the difference between themineral-self-binding pigmentary particles binder pair on the one hand,and for a simple mixture on the other hand, is illustrated using adifferential thermal analysis machine (ATD) TGA/SDTA 851e, sold by thecompany METTLER TOLEDO™. The heating conditions being: a rise intemperature of 5° C. per minute, from 25 C to 350° C.

In comparison, the same measurements were made on the pure products(marble and binder).

FIG. 1 illustrates the difference between the mineral-self-bindingpigmentary particles binder pair according to the invention, and asimple mineral-binder mixture

To demonstrate the suitability for the self-binding character of thepigmentary particles thus obtained, tablets were formulated using amembrane filtration process.

A machine of the high-pressure filter press type is used, manufacturedfrom a hollow steel tube. The said tube is closed at the top by a lidand contains the filtration membrane at the bottom.

A volume of 80 ml is then introduced of either a suspension containingonly the inorganic matter (which is used to manufacture the referencesamples), or of a suspension according to the invention (which is usedto manufacture the samples for testing).

A constant pressure of 15 bar is then applied, which enables the waterto be eliminated, until a tablet 20 mm thick is obtained.

The samples are then dried in free air for 1 week.

The device and method used are described in detail in the document“Modified calcium carbonate coatings with rapid absorption and extensiveliquid update capacity” (Colloids and Surfaces A, 236 (1-3), 2003, pp.91-102),

The quasi-cylindrical solid blocks of pigmentary particles were groundusing a disk mill (Jean Wirtz, Phoenix 4000) in the form of disk-shapedsamples of diameter 25 mm and of approximate thickness 15 mm. Theprocedure is described in the document “Fluid transport into porouscoating structures: some novel findings” (Tappi Journal, 83 (5), 2000,pp. 77-78).

The samples obtained underwent a crush resistance test on a Zwick-Roelltension machine with a WN158988 control unit, using a rod/flat system(with a hemispherical end). The force of the cell is 20 kN.

The samples are crushed at a speed of 3 mm.min⁻¹ over a length of 10 mm.The values of the force for a deformation of 2 mm are illustrated inFIG. 2 for this example and the following examples. FIG. 2 illustratesthe self-binding power for the self-binding pigmentary particlesaccording to the invention: measurement of the force in the crush testfor a 2 mm deformation for:

-   -   samples of a suspension of self-binding pigmentary particles        according to the invention,    -   samples formulated according to the method described in example        1 from an aqueous suspension containing only the mineral matter        used in the invention (2)

FIG. 2 shows clearly that the process according to the invention enablesself-binding pigmentary particles to be obtained in which theinter-particular cohesive forces between the mineral particles are muchhigher than in the case of the initial mineral matter. This phenomenonis observed for example 1, but also for examples 2 to 4 which will bedescribed subsequently.

Tables 1 and 1 bis indicate the granulometric distribution of theparticles according to the invention, and of the initial mineralparticles. TABLE 1 granulometric distribution as measured using aMasterSizer ™ S granulometer sold by the company MALVERN ™ in the caseof the suspension of self-binding pigmentary particles obtained usingthe process according to the invention (1), using a Sedigraph ™ 5100sold by the company MICROMERITICS in the case of a suspension of initialinorganic matter (2). Quantity of Quantity of Size of particlesparticles by particles by (μm) volume (%) (1) volume (%) (2) <71 100 100<45 100 100 <25 100 100 <10 100 99 <5 100 96 <2 98 84 <1 85 59 <0.7 71<0.5 52 24 <0.2 4 6 <0.1 0 1

TABLE 1 bis value of the parameters D₅₀ (%) and D₉₀ (%) (diametermeasurements for which respectively 50% and 90% by volume of theparticles having a diameter of less than or equal to this value) for:the self-binding pigmentary particles obtained using the processaccording to the invention (1) the initial inorganic matter (2) 1 2 D₅₀(%) 0.48 0.85 D₉₀ (%) 1.21 —

Tables 1 and 1 bis demonstrate a notable reduction of the particlesizes, in the case of the self-binding pigmentary particles obtainedaccording to the invention, relative to the initial inorganic matter.

EXAMPLE 2

This example concerns the process for preparing self-binding pigmentaryparticles in an aqueous suspension from marble and from astyrene-butadiene binder.

To accomplish this, the first stage a) of the process consists informing an aqueous suspension of marble having an average particlediameter of 0.85 μm by putting the marble into suspension in water at adry matter content by weight equal to 20%.

For the second stage b) of the process, an aqueous suspension of binderDL 966 of DOW CHEMICALS is used at a content by weight of 50%.

Stage c) of the process is then undertaken by co-grinding the marblesuspension obtained in stage a) with the suspension of binder obtainedin stage b) with the same equipment as that used in example 1.

On conclusion of the grinding (30 minutes) a sample of the obtainedsuspension of self-binding pigmentary particles is removed in a flask.The granulometry of the suspension is measured using a MasterSizer™ Sgranulometer sold by the company MALVERN™ and is such that 75% of theparticles have an average diameter of less than or equal to 1 μm.

The product thus obtained is an aqueous suspension of self-bindingpigmentary particles having a dry matter by weight content of calciumcarbonate equal to 21%, an average particle diameter equal to 0.65 μmmeasured using a MasterSizer™ S granulometer sold by the companyMALVERN™ and a calcium carbonate/binder ratio equal to 100/10 by weightproportions.

The binding power of the said particles was measured by a crush testaccording to the method described in example 1, and is illustrated inFIG. 2. The latter shows that the process according to the inventionenables self-binding pigmentary particles to be obtained in which theinter-particular cohesive forces between the mineral particles are muchhigher than in the case of the initial mineral matter.

Tables 2 and 2 bis indicate the granulometric distribution of theparticles according to the invention, and of the initial mineralparticles. TABLE 2 granulometric distribution as measured using aMasterSizer ™ S granulometer sold by the company MALVERN ™ in the caseof the suspension of self-binding pigmentary particles obtained usingthe process according to the invention (1), using a Sedigraph ™ 5100sold by the company MICROMERITICS in the case of a suspension of initialinorganic matter (2) Quantity of Quantity of Size of particles particlesby particles by (μm) volume (%) (1) volume (%) (2) <71 100 100 <45 100100 <25 100 100 <10 100 99 <5 100 96 <2 98 84 <1 75 59 <0.7 54 <0.5 3524 <0.2 5 6 <0.1 1 1

TABLE 2 bis value of the parameters D₅₀ (%) and D₉₀ (%) (diametermeasurements for which respectively 50% and 90% by volume of theparticles having a diameter of less than or equal to this value) for:the self-binding pigmentary particles obtained using the processaccording to the invention (1) the initial inorganic matter (2) 1 2 D₅₀(%) 0.65 0.85 D₉₀ (%) 2.00

Tables 2 and 2 bis demonstrate a notable reduction of the particlesizes, in the case of the self-binding pigmentary particles obtainedaccording to the invention, relative to the initial inorganic matter.

EXAMPLE 3

This example concerns the process for preparing self-binding pigmentaryparticles in an aqueous suspension from precipitated calcium carbonate(PCC) and two suspensions of binders.

To accomplish this, the first stage a) of the process consists informing an aqueous suspension of precipitated calcium carbonate havingan average diameter of 1.8 μm by putting the precipitated calciumcarbonate into suspension in water at a dry matter content by weightequal to 20%.

For the second stage b) of the process, use is made of a first aqueoussuspension of Acronal™ S728 binder sold by the company BASF at a drymatter content by weight equal to 20%, and a second aqueous suspensionof Polygen™ WE4 binder sold by the company BASF at a dry matter contentby weight equal to 20%.

The three suspensions are then co-ground with the same equipment as thatof example 1.

On conclusion of the grinding (30 minutes) a sample of the obtainedsuspension of self-binding pigmentary particles is removed in a flask.The granulometry of the suspension is measured using a MasterSizer™ Sgranulometer sold by the company MALVERN™ and is such that 83% of theparticles have an average diameter of less than or equal to 1 μm.

The product thus obtained is an aqueous suspension of self-bindingpigmentary particles having a dry matter by weight content ofprecipitated calcium carbonate equal to 20%, an average particlediameter equal to 0.53 μm measured using a MasterSizer™ S granulometersold by the company MALVERN™ and a PCC/Acronal™ S728/Polygen™ WE4 ratioequal to 100/9.5/0.5 by dry matter weight proportions.

The binding power of the said particles was measured by a crush testaccording to the method described in example 1, and is illustrated inFIG. 2. The latter shows that the process according to the inventionenables self-binding pigmentary particles to be obtained in which theinter-particular cohesive forces between the mineral particles are muchhigher than in the case of the initial mineral matter.

Tables 3 and 3 bis indicate the granulometric distribution of theparticles according to the invention, and of the initial mineralparticles. TABLE 3 granulometric distribution as measured using aMasterSizer ™ S granulometer sold by the company MALVERN ™ in the caseof the suspension of self-binding pigmentary particles obtained usingthe process according to the invention (1), using a Sedigraph ™ 5100sold by the company MICROMERITICS in the case of a suspension of initialinorganic matter (2) Quantity of Quantity of Size of particles particlesby particles by (μm) volume (%) (1) volume (%) (2) <71 100 100 <45 100100 <25 100 100 <10 100 100 <5 100 96 <2 98 59 <1 83 38 <0.7 65 29 <0.547 21 <0.2 9 5 <0.1 1 1

TABLE 3 bis value of the parameters D₅₀ (%) and D₉₀ (%) (diametermeasurements for which respectively 50% and 90% by volume of theparticles having a diameter of less than or equal to this value) for:the self-binding pigmentary particles obtained using the processaccording to the invention (1) the initial inorganic matter (2) 1 2 D₅₀(%) 0.53 1.57 D₉₀ (%) 2.00 6.0

Tables 3 and 3 bis demonstrate a notable reduction of the particlesizes, in the case of the self-binding pigmentary particles obtainedaccording to the invention, relative to the initial inorganic matter.

EXAMPLE 4

This example concerns the process for preparing self-binding pigmentaryparticles in aqueous suspension from a mixture of talc and titaniumdioxide and a solution of binders obtained by mixing starch andpolyvinylic alcohol.

To accomplish this, the first stage a) of the process according to theinvention consists in producing an aqueous suspension of talc having anaverage diameter of 13 μm and of titanium dioxide having an averagediameter of less than 0.2 μm, by putting in suspension the talc and thetitanium dioxide (in a 1:1 ratio by dry weight) in water at a dry matterweight content equal to 48%.

Stage b) of the process according to the invention is undertaken bydiluting an aqueous suspension of polyvinylic alcohol Mowiol™ 4-88 soldby the company OMYA Peralta until a dry matter content by weight equalto 34% is reached, whilst stirring for 20 minutes, at a temperature of90° C., and whilst preparing a solution of starch at a dry mattercontent by weight equal to 22%, whilst stirring for 20 minutes, at atemperature of 90° C.

Following this, the resulting suspension is co-ground with the sameequipment as in example 1.

On conclusion of the grinding (30 minutes) a sample of the obtainedsuspension of self-binding pigmentary particles is removed in a flask.The granulometry of the suspension is measured using a MasterSizer™ Sgranulometer sold by the company MALVERN™ and is such that 28% of theparticles have an average diameter of less than or equal to 1 μm.

The product thus obtained is an aqueous suspension of self-bindingpigmentary particles having a dry matter by weight content of talc andtitanium dioxide equal to 37%, an average particle diameter equal to 46pm measured using a MasterSizer™ S granulometer sold by the companyMALVERN™ and a talc and titanium dioxide/polymeric binders ratio equalto 100/10 by weight proportions.

The binding power of the said particles was measured by a crush testaccording to the method described in example 1, and is illustrated inFIG. 2. The latter shows that the process according to the inventionenables self-binding pigmentary particles to be obtained in which theinter-particular cohesive forces between the mineral particles are muchhigher than in the case of the initial mineral matter.

Tables 4 and 4 bis indicate the granulometric distribution of theparticles according to the invention, and of the initial mineralparticles. TABLE 4 granulometric distribution as measured using aMasterSizer ™ S granulometer sold by the company MALVERN ™ in the caseof the suspension of self-binding pigmentary particles obtained usingthe process according to the invention (1), using a Sedigraph ™ 5100sold by the company MICROMERITICS in the case of a suspension of initialinorganic matter (2) Quantity of Quantity of Size of particles particlesby particles by (μm) volume (%) (1) volume (%) (2) <71 100 99 <45 97 91<25 86 70 <10 54 41 <5 37 32 <2 29 27 <1 28 25 <0.7 27 23 <0.5 24 20<0.2 5 6 <0.1 1

TABLE 4 bis value of the parameters D₅₀ (%) and D₉₀ (%) (diametermeasurements for which respectively 50% and 90% by volume of theparticles having a diameter of less than or equal to this value) for:the self-binding pigmentary particles obtained using the processaccording to the invention (1) the initial inorganic matter (2) 1 2 D₅₀(%) 8.9 14.3 D₉₀ (%) 9.0 15.0

Tables 4 and 4 bis demonstrate a notable reduction of the particlesizes, in the case of the self-binding pigmentary particles obtainedaccording to the invention, relative to the initial inorganic matter.

EXAMPLE 5

This example illustrates a variant of the process of preparationaccording to the invention for pigmentary self-linking particles inaqueous suspension from marble and from two binding agents insuspension.

To do this, we produce with the same material and the same operatingconditions as in example 1, the aqueous suspension of self-bindingpigmentary particles from example 1, having a content in weight of drymaterial of calcium carbonate equal to 20%, an average particle diameterof 0.50 μm as measured by a MasterSizer™ S, and a marble/Acronal™S728/Polygen™ WE4 equal to 100/9, 5/0, 5 in parts in dry materialweight.

Once this aqueous suspension of self-binding pigmentary particles isobtained, it is put in a Rouan YXY centrifuge rotating at 5,500 rpm soas to increase its dry material concentration.

After 6 minutes in the centrifuge, the resulting aqueous suspension has58% dry material content.

Once obtained, this concentrated aqueous suspension of self-bindingpigmentary particles is dispersed using a Pendraulik™ agitator at 300rpm and adding 0.5% dry weight of the dry weight of pigmentary particlesof a wetting agent, styrene copolymer/butyl acrylate/methacrylicacid/acrylic acid and 0.1% dry weight of the dry weight of pigmentaryparticles of a dispersing agent, acrylic acid copolymer/maleicanhydride, then the quantity of water needed to obtain a 55%concentration of dry material.

The resulting Brookfield™ viscosity figure is 106 mPa·s at 100 rpm.

EXAMPLE 6

This example again illustrates another variant of the process accordingto the invention.

To do this, we produce with the same material and the same operatingconditions as in example 1, the aqueous suspension of self-bindingpigmentary particles from example 1, having a content in weight of drymaterial of calcium carbonate equal to 20%, an average particle diameterof 0.50 μm as measured by a MasterSizer™ S, and a marble/Acronal™S728/Polygen™ WE4 equal to 100/9, 5/0, 5 in parts in dry materialweight.

Once obtained this suspension of self-binding pigmentary particles, afilter press is used to raise the suspension's dry materialconcentration up to 65.4%.

Once obtained this concentrated aqueous suspension of self-bindingpigmentary particles, we disperse it using a Pendraulik™ agitator at aneven speed of 3,000 rpm and consecutively adding 0.17% in dry weight ofthe Tamol™ NN9104 wetting agent and 0.59% in dry weight of the CoatexP70 dispersing agent, in dry weight terms of pigmentary particles.

After 14 days storage the Brookfield™ viscosity index is 1630 mPa·s at100 rpm.

1. A process for the preparation of self-binding pigmentary particles,dry or in aqueous suspension or dispersion, comprising the followingstages: a) forming one or more aqueous suspensions of at least oneinorganic matter and introducing it or them into a mill with a view tostage c) b) forming or taking one or more aqueous solutions orsuspensions or emulsions of at least one binder and introducing it orthem into a mill with a view to stage c) c) co-grinding the aqueoussuspension or suspensions obtained in stage a) with the aqueoussolutions or suspensions or emulsions obtained in stage b) so as toobtain an aqueous suspension of self-binding pigmentary particles d)possibly co-grinding the aqueous suspension obtained in stage c) withone or more aqueous solutions or suspensions or emulsions of at leastone binder e) possibly drying the aqueous suspension obtained in stagec) or in stage d)
 2. A process according to claim 1 characterized inthat the aqueous suspension or suspensions of inorganic matter formed instage a) contain from 1% to 80% by dry weight of inorganic matter.
 3. Aprocess according to claim 2 characterized in that the aqueoussuspension or suspensions of inorganic matter formed in stage a) containfrom 15% to 60% by dry weight of inorganic matter.
 4. A processaccording to claim 1 characterized in that the said aqueous suspensionor suspensions of inorganic matter formed in stage a) contain one ormore inorganic matter.
 5. A process according to claim 4 characterizedin that the said inorganic matter are chosen from among the metallicoxides, the hydroxides, the sulphites, the silicates and the carbonates,such as calcium carbonate, the dolomites, kaolin, talc, gypsum, titaniumdioxide, satin white or aluminium trihydroxide and their mixtures.
 6. Aprocess according to claim 5 characterized in that the said inorganicmatter is chosen from among the calcium carbonates in the natural formor in the precipitated form or their mixtures.
 7. A process according toclaim 6 characterized in that the said inorganic matter is a naturalcalcium carbonate chosen from among chalk, marble, calcite, or theirmixtures.
 8. A process according to claim 1 characterized in that theaqueous solutions or suspensions or emulsions of at least one binderformed in stage b) contain from 1% to 50% by weight of at least onebinder, and more preferentially from 5% to 20% by weight of at least onebinder.
 9. A process according to claim 1 characterized in that thebinder or binders of stage b are chosen from among the semi-crystallinelatexes, or from among the latexes in emulsion or the solutions ofsoluble binders such as polyvinylic alcohol, polyvinyl acetate, starch,casein, proteins, carboxymethyl cellulose (CMC), ethyl hydroxyethylcellulose (EHEC), or their mixtures.
 10. A process according to claim 9characterized in that the semi-crystalline latexes are preferentiallychosen from among the emulsions of polyethylene waxes or copolymers intheir neutralised form of polyethylene with other monomer units such asacrylic acid or other monomers or their mixtures.
 11. A processaccording to claim 9 characterized in that the emulsion latexes arechosen from among the copolymers of acrylic esters.
 12. A processaccording to claim 1 characterized in that the suspension formed instage c) has a ratio between inorganic matter and binders contained inthe suspension obtained between 99 and 1 expressed in weightproportions.
 13. A process according to claim 12 characterized in thatthe ratio between the inorganic matter and the binders contained in thesuspension obtained is between 70 and 30 expressed as weightproportions.
 14. A process according to claim 1 characterized in thatthe self-binding pigmentary particles thus formed have an averageparticle diameter of between 0.1 μm and 10 μm measured using aMasterSizer™ S granulometer sold by the company MALVERN.
 15. A processaccording to claim 14 characterized in that the self-binding pigmentaryparticles thus formed have an average particle diameter of between 0.1μm and 2 μm measured using a MasterSizer™ S granulometer sold by thecompany MALVERN.
 16. The procedure according to claim 1 characterized inthat it includes the following stages: a) forming one or more aqueoussuspensions containing at least one inorganic material in a grinder inview of stage c) b) forming or taking one or more solutions orsuspensions or emulsions containing at least one binder in a grinder inview of stage c) c) co-grinding the suspension or suspensions obtainedat stage a) with the solutions or aqueous suspensions or emulsionsobtained at stage b) so as to obtain an aqueous suspension ofself-binding pigmentary particles d) possibly co-grinding the aqueoussuspension obtained at stage c) with one or more solutions or aqueoussuspensions or emulsions of at least one binder f) increasing theconcentration of the aqueous suspension obtained at stage c) or d)through thermal or mechanical concentration; g) dispersing the aqueoussuspension obtained at stage f) through using at least one dispersingagent and/or at least one wetting agent.
 17. A process according toclaim 16 characterized in that the dispersing agent or agents are chosenfrom among polymers and/or acrylic or vinylic or allylic copolymers,such as homopolymers or copolymers in their totally acidic or partiallyor totally neutralised forms by neutralising agents containingmonovalent or polyvalent cations or amines or their mixtures, from atleast one of the monomers such as the acrylic and/or methacrylic,itaconic, crotonic, fumaric acids, the maleic anhydride or isocrotonic,aconitic, mesaconic, sinapic, undecylenic acid, angelic acid and/ortheir respective esters such as the acrylates or methacrylates of alkyl,aryl, alkylaryl, arylalkyl and in particular ethyl acrylate, butylacrylate, methyl methacrylate, sofonic acrylamido methyl propane acid,acrylamide and/or methacrylamide, carylate phosphate of glycol ethylene.methacrylate phosphate of glycol ethylene, acrylate phosphate of glycolpropylene, methacrylate phosphate of glycol propylene, chlorine orammonium trimethyl propyl methacrylamid sulphate, as well as theiracrylate and acrylamide equivalents, quaternised or not, and/ordimethyldiallyl chlorate, vinylpyrrolidone, vinylcaprolactame,diisobutylene, vinyl acetate, styrene, alpha-methyl-styrene, styrenesodium sulfonate, vinylmethylether, allyllamine or chosen from at leastone of the said monomers or their mixtures, polymerised in the presenceof at least one mineral material.
 18. A process according to claim 16characterized in that from 0.01% to 2% by weight of at least onedispersing agent is added.
 19. A process according to claim 16characterized in that from 0.01% to 5% by weight of at least one wettingagent is added.
 20. An aqueous suspension of self-binding pigmentaryparticles containing at least one inorganic matter and at least onebinder characterized in that it is obtained by the process according toclaim
 1. 21. An aqueous suspension of self-binding pigmentary particlescontaining at least one inorganic matter and at least one bindercharacterized in that it is obtained by the process according to claim1, characterized in that it is self-binding.
 22. An aqueous suspensionof self-binding pigmentary particles containing at least one inorganicmatter and at least one binder according to claim 20 characterized inthat it contains between 5% and 80% by weight of inorganic matter,between 1% and 30% by weight of binders, and between 19% and 94% byweight of water, and preferentially, in that it contains between 20% and40% by weight of inorganic matter, between 5% and 20% by weight ofbinders, and between 40% and 75% by weight of water.
 23. An aqueousdispersion of self-binding pigmentary particles containing at least oneinorganic matter and at least one binder characterized in that it isobtained by the process according to claim
 16. 24. An aqueous dispersionof self-binding pigmentary particles containing at least one inorganicmatter and at least one binder characterized in that it is obtained bythe process according to claim 16, characterized in that it isself-binding.
 25. An aqueous dispersion of self-binding pigmentaryparticles containing at least one inorganic matter and at least onebinder according to claim 23, characterized in that it contains between5% and 80% by weight of inorganic matter, between 1% and 30% by weightof binders, between 19% and 94% by weight of water, between 0.01% and 2%by weight of at least one dispersing agent and/or between 0.01% and 5%by weight of at least one wetting agent, and preferentially in that itcontains between 20% and 40% by weight of inorganic matter, between 5%and 20% by weight of binders, between 40% and 75% by weight of water,between 0.01% and 2% by weight of at least one dispersing agent and/orbetween 0.01% and 5% by weight of at least one wetting agent.
 26. Aprocess according to claim 1 characterized in that the self-bindingpigmentary particles formed in stage e) contain from 70% to 97.5% byweight of at least one inorganic matter and from 2.5% to 30% by weightof at least one binder.
 27. A process according to claim 26characterized in that the self-binding pigmentary particles formed instage e) contain from 85% to 95% by weight of at least one inorganicmatter and from 5% to 15% by weight of at least one binder.
 28. Aprocess according to claim 1 and characterized in that the averagediameter of the self-binding pigmentary particles formed in stage e) isbetween 5 Jlm and 100 Jim as measured using a MasterSizer™ Sgranulometer sold by the company MALVERN.
 29. A process according toclaim 28 characterized in that the average diameter of the self-bindingpigmentary particles formed in stage e) is between 10 gm and 30 pm asmeasured using a MasterSizer™ S granulometer sold by the companyMALVERN.
 30. Self-Binding pigmentary particles, containing at least oneinorganic matter and at least one binder, obtained by the processaccording to claim 1, characterized in that they contain from 70% to97.5% by weight of at least one inorganic matter and from 2.5% to 30% byweight of at least one binder, and preferentially in that they containbetween 85% and 95% by weight of at least one inorganic matter and from5% to 15% by weight of at least one binder.